Field of the Invention
The present invention relates to a linear motor and, more particularly, to a linear motor control apparatus of a linear motor of a moving magnet type and a linear motor control system.
Description of the Related Art
A linear motor of a moving magnet type has such a construction that a magnet is arranged in a truck serving as a needle and a coil is arranged in a stator, respectively, and is suitable for conveyance of a long stroke as compared with a linear motor of a moving coil type in which an electric wire is connected to a truck. In such a moving magnet type linear motor, when a driving stroke longer than a size of needle is necessary, a plurality of coils corresponding to a stroke length are necessary. Generally, the moving magnet type linear motor has such a construction that a plurality of coils are arranged and connected to a current controller so that current control by three phases can be made (refer to Japanese Patent No. 2831166). According to such a construction, if all of the three-phase coils are connected to the same current controller so that those phases are serially connected, a thrust can be generated. However, it is difficult to individually control the plurality of trucks on the same conveying path.
Therefore, a coil unit comprising a plurality of coils is constructed, a linear motor module having a motor controller for controlling a position of one truck is constructed so as to correspond to one coil unit, and a plurality of trucks are individually controlled.
Generally, such a construction that a plurality of linear motor modules are continuously arranged, a long stroke conveyance is attained, and the plurality of trucks on the same orbit are controlled is known.
In a conveying apparatus for FA (Factory Automation), it is required that a plurality of trucks are arranged at a high density, the truck is moved at a high speed, the truck is stopped at a high precision, and a restriction to a stop position of the truck is small.
However, in such a construction that the linear motor modules are simply arranged, when one truck stops at a boundary position between the adjacent linear motor modules, the truck stops at a boundary position between the adjacent coil units. In this case, since the truck is simultaneously controlled from two motor controllers for respectively controlling the adjacent coil units, it is difficult to stop the truck at a high precision.
In the case of controlling one truck by using the motor controller of one of the adjacent linear motor modules, although the truck can be stopped by driving one of the coil units, a thrust which is applied to the truck is reduced to the half. On the other hand, in order to allow the truck to obtain a thrust which is equal to that in the case where both of the adjacent coil units were driven, it is necessary to supply a double driving current to one coil unit and costs of an electric circuit are high. Therefore, such a construction is undesirable.
According to Japanese Patent No. 2831166, a thrust command serving as current control information is generated by one position detector and one motor controller and the same thrust command is transmitted to a plurality of current controllers, thereby driving a plurality of continuous coil units and controlling one truck. However, according to such a construction, although the truck can be stopped at the boundary position between the coil units while keeping the thrust which is applied to one truck, a plurality of trucks cannot be controlled.